Presentation
Increasing infrapatellar pain and tenderness.
Patient Data
Knee joint alignment is normal. No joint effusion or loose intra-articular body identified. The anterior cruciate ligament and posterior cruciate ligament are intact.
The lateral meniscus is discoid and there is a undisplaced horizontal cleavage tear through the body and anterior horn. The anterior horn tear communicates with a large complex septated parameniscal cyst which protrudes into Hoffa's fat pad. It measures 37 x 25 x 16 mm (transverse by AP by cc). The lateral collateral ligament is normal. Cartilage of the lateral compartment is normal. The popliteus tendon and posterolateral corner structures are normal.
The medial meniscus is intact. The medial collateral ligament is normal. Cartilage of the medial compartment is normal.
Patellofemoral alignment and cartilage is normal. The quadriceps tendon and patellar ligament are normal. Extensor retinaculum is unremarkable. The iliotibial band is normal.
No abnormal bone marrow signal or osseous lesion. The popliteal fossa is normal.
Conclusion:
Large parameniscal cyst protruding into Hoffa's fat pad arising from the undisplaced horizontal cleavage tear of the body and anterior horn of the discoid lateral meniscus.